Liquid crystal display is a passive display, which cannot emit light directly, but only uses light from the surrounding environment. The liquid crystal display (LCD) only requires very little energy to display patterns or characters, and thus has become a preferred display mode due to low power consumption and small size thereof.
The liquid crystal material used in the liquid crystal display is an organic matter comprising both liquid phase and solid phase. Molecules of the liquid crystal material each having a rod-like structure, and are usually aligned in a liquid crystal cell in parallel. However, the orientations of the liquid crystal molecules can be changed in an electric field. For a positive twist nematic liquid crystal display (TN-LCD), when no voltage is applied to an electrode, the liquid crystal display (LCD) is in an off state. In this case, light can pass through the LCD, and thus the LCD appears bright. When voltage is applied to the electrode, the LCD is turned on. In this case, the liquid crystal molecules are aligned with the long axes thereof being oriented in the direction of the electric field. Light cannot pass through the LCD, and thus the LCD appears dark. Voltage can be selectively applied to the electrode, so that different images can be displayed. In a super twist nematic liquid crystal display (STN-LCD), because the twisted angle of the liquid crystal is larger, the contrast ratio thereof is better and the viewing angle is wider.
A liquid crystal display comprises a liquid crystal cell, which is formed by two conductive glass sheets and filled with liquid crystal. The four sides of the liquid crystal cell are sealed with sealing material, which is generally a glue made of epoxy resin. Each of the exterior sides of the liquid crystal cell is provided with a polarizer.
A distance between the upper and the lower glass sheets in the liquid crystal cell, which is usually called a cell thickness, is generally several micrometers. The smallest discernible diameter to the naked eyes is a few tens of micrometers. Transparent indium tin oxide (ITO) conductive film, i.e., display electrode, is coated on an interior area on each of the upper and the lower glass sheets, corresponding to the image display area. External electric signal is transmitted to the liquid crystals through the display electrodes.
An orientation layer covers the entire display area on the interior side of each of the glass sheets in the liquid crystal cell. The liquid crystal molecules can be aligned in a specific direction under the action of the orientation layer, which is usually a thin layer of macromolecule organic treated with a rubbing process. The orientation layer can also be formed through vacuum evaporation of silicon oxide thin film on the glass surface for a certain angle.
A twist nematic (TN) liquid crystal display is filled with positive nematic liquid crystals. The orientation of the liquid crystal molecules means that the long rod-like liquid crystal molecules are aligned in a fixed direction in parallel with the surfaces of the glass sheets, and the long axes thereof are along a surface orientation. The surface orientation of the upper glass sheet is perpendicular to that of the lower glass sheet. In this case, the orientations of the liquid crystal molecules along a direction perpendicular with respect to the glass sheets gradually twist, i.e., the orientation of liquid crystal molecules on the lower glass sheet twists for 90 degrees with respect to that of corresponding liquid crystal molecules on the upper glass sheet. This is where the name of the twist nematic liquid crystal display comes from.
In fact, liquid crystal molecules close to the surface of the glass sheet are not completely parallel therewith, but rather form an angle with respect to the surface of the glass sheet. Such an angle is called a pre-tilt angle, being in a range of 1° to 2°.
A polarizer is arranged on each of the exterior surfaces of the two glass sheets in the liquid crystal cell. Polarization axes of the two polarizers are parallel with each other (normally black mode with dark background and bright character) or perpendicular to each other (normally white mode with bright background and dark character), and each are parallel with the surface orientation of the corresponding glass sheet. The polarizers are usually formed from macromolecular plastic film under certain process conditions.
Due to the intrinsic factors of the liquid crystal display, an image observed from different positions of the liquid crystal display would always be different. As a result, an image, which is normal when being observed at a center viewing angle, would be abnormal when being observed at a wide angle. Such a phenomenon is called color shift with large viewing angle. In the prior art, the structure as shown in FIG. 1 is generally adopted. That is, one sub pixel is divided into a main sub pixel 1 and a secondary sub pixel 2, which are respectively provided with different electric potentials under a specific gray scale. In this case, there are two orientations of the liquid crystal molecules under the same gray scale, thereby the difference between brightness under a wide viewing angle and that under a center viewing angle can be relatively small. Currently, most manufacturers use the above design of sub pixels. However, the display effect of such design is still limited. Therefore, in order to obtain better display quality under wide viewing angle, a new design is proposed according to the present disclosure.